1. Field of the Invention
The present invention relates to a Code Division Multiple Access (CDMA) system, and more particularly, to an apparatus and method for acquiring multi-user signal synchronization in a CDMA system.
2. Background of the Related Art
Generally, a receiver of a base station or terminal using CDMA mode is designed to correlate with codes for asynchronous signal transmission. Such a CDMA system employs a matched filter receiver, and requires strict power control in order to avoid potential problems, such as interference due to multiple users in the same cell.
A matched filter is a linear filter. Thus, the difference between the square mean of a signal element and the square mean of a noise element is maximized at a certain point of an output, with respect to an input in which a correlation noise is overlapped with a desired signal element. In addition, a seed is a constant used as an initial value of a pseudo random number generator. That means that the seed of an initial random number generates the next result, and the generated result acts as a seed.
FIG. 1 shows one example of a block construction of an apparatus for acquiring multi-user signal synchronization in a CDMA system in the related art.
As illustrated therein, the apparatus includes a plurality of user units 1–N for transmitting pilot signals using different Pseudo Noise (PN) seeds. It also includes a plurality of matched filters 11˜(10+N) for acquiring a signal synchronization of each of the user units 1–N using a coefficient generated with a PN seed that is identical to the coefficient of each user unit 1–N. Finally, it includes a plurality of demodulators 21˜(20+N) for demodulating signals of the corresponding user units according to the synchronizations acquired from the corresponding matched filters 11˜(10+N).
In operation, when N number of users are present, the N number of users each have a different PN seed. Thus, the N number of user units 1–N transmit pilot signals using the associated PN seed. A CDMA receiver has N number of matched filters 11˜(10+N), which correspond to the N number of user units 1–N. The corresponding matched filter receives pilot signals from each of the user units 1–N.
That is, the N number of matched filters 11˜(10+N) each have the same PN seed as that used in corresponding ones of the N number of user units 1–N. When a pilot signal is received from a given user unit 1–N the matched filter corresponding to the user unit's PN seed is operated, thereby acquiring synchronization.
The related art system has many problems. For example, when there are many users, the apparatus for acquiring multi-user signal synchronization in a CDMA system in the related art requires an increased number of matched filters in proportion to the number of users. Therefore, the problem arises that the size and volume of the CDMA receiver are increased, and the cost is also increased.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.